The present invention relates to a method and apparatus for suppressing aeroengine condensation trails (contrails).
Recent climate assessments have stressed the importance of the radiative effects of contrails on global warming. Perturbations in the planetary radiation balance are enforced by the emission of greenhouse gases, aerosols, contrails and aviation induced cirrus clouds. The radiative forcing from contrails and cirrus clouds might be larger than the radiative forcing from all other aircraft emissions combined.
In U.S. Pat. No. 3,517,505 a method of suppressing contrails comprises the steps of preheating a hydroscopic material to decomposition temperatures and introducing the preheated decomposition material into the exhaust stream of said aircraft, said preheated decomposed hydroscopic material being introduced in an amount sufficient to produce a large number of small particles to provide nuclei upon which the water produced by burning jet fuel can condense to prevent the formation of visible contrails. The decomposed hydroscopic material may be either chlorosulfonic acid or sulphur trioxide. The increased number of nuclei produces a higher number of smaller ice crystals that are not visible and can alter the radiative properties of the contrail.
U.S. Pat. No. 5,005,355 discloses a method of suppressing the formation of contrails from the exhaust of an engine operating in cold temperatures including the steps of providing a combined nucleating agent and freeze-point depressant selected from the group of water soluble monohydric, dihydric, trihydric or other polyhydric alcohols, or mixtures thereof, forming the solution into a vapour, and injecting the solution into the exhaust of the engine. The solution may include a non-corrosive surfactant. Another solution may include an organic or an inorganic nucleating agent, or mixtures thereof, in monohydric, dihydric or polyhydric alcohols, or mixtures thereof, and in addition may contain one or more surfactants. Effectively, the freezing point of water is depressed to avoid contrail formation.
These earlier attempts to suppress contrails are disadvantaged because chemicals are used and discharged into the atmosphere, the chemicals have to be transported implying a weight and space penalty, there is an engine efficiency loss due to the delivery mechanisms being in the exhaust ducts, the contrails are not suppressed with only their visibility altered and therefore the smaller contrail particles may cause global dimming. The environmental impact of the chemicals used in these earlier attempts prevent their utilisation for commercial purposes.
Therefore it is an object of the present invention to provide an aeroengine that reduces or eliminates condensation trails and/or cirrus cloud formations.